Meaning of Idiom 'Horse of a Different Color'

When we say something is a horse of a different color we mean that it is a completely different issue; an unrelated matter.

Usage

"I thought you just wanted kitchen cabinets," said the contractor, "not a full remodel. That's a horse of a different color."

"His actions were not technically illegal," said Mr. Briggs, "but his intent, well that's a horse of a different color."

"I don't mind Becky coming with us but her friend Jane is a horse of another color."

Origin

The precise allusion of this idiom is unknown. It may have to do with horse breeding since it has long been observed that if you want to breed a certain color horse, you could not mate a mare to a stud with a completely different color coat or you would likely get a "horse of a different color."

However, the opposite idiom is seen in Shakespeare's Twelfth Night:

Maria: My purpose is, indeed, a horse of that colour.
Sir Andrew: An your horse now would make him an ass.

It is suggested, then, that Shakespeare coined "a horse of that color" to refer to something that was the same matter, and that the idiom evolved to refer to completely unrelated matters. However, Shakespeare's use of the phrase may simply mean that the idiom under discussion was already in use. However, it does not appear to have been in widespread use until the mid-1800's.